/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.base;

import com.google.caliper.BeforeExperiment;
import com.google.caliper.Benchmark;
import com.google.caliper.Param;

/**
 * Microbenchmark for {@link com.google.common.base.Strings#repeat}
 *
 * @author Mike Cripps
 */
public class StringsRepeatBenchmark
{
    @Param({"1", "5", "25", "125"})
    int count;

    @Param({"1", "10"})
    int length;

    private String originalString;

    @BeforeExperiment
    void setUp()
    {
        originalString = Strings.repeat("x", length);
    }

    @Benchmark
    void oldRepeat(long reps)
    {
        for (int i = 0; i < reps; i++)
        {
            String x = oldRepeat(originalString, count);
            if (x.length() != (originalString.length() * count))
            {
                throw new RuntimeException("Wrong length: " + x);
            }
        }
    }

    private static String oldRepeat(String string, int count)
    {
        // If this multiplication overflows, a NegativeArraySizeException or
        // OutOfMemoryError is not far behind
        final int len = string.length();
        final int size = len * count;
        char[] array = new char[size];
        for (int i = 0; i < size; i += len)
        {
            string.getChars(0, len, array, i);
        }
        return new String(array);
    }

    @Benchmark
    void mikeRepeat(long reps)
    {
        for (int i = 0; i < reps; i++)
        {
            String x = mikeRepeat(originalString, count);
            if (x.length() != (originalString.length() * count))
            {
                throw new RuntimeException("Wrong length: " + x);
            }
        }
    }

    private static String mikeRepeat(String string, int count)
    {
        final int len = string.length();
        char[] strCopy = new char[len * Integer.highestOneBit(count)];
        string.getChars(0, len, strCopy, 0);

        char[] array = new char[len * count];

        int strCopyLen = len;
        int pos = 0;
        while (count != 0)
        {
            if ((count & 1) != 0)
            {
                System.arraycopy(strCopy, 0, array, pos, strCopyLen);
                pos += strCopyLen;
            }
            count >>= 1;
            if (count != 0)
            {
                System.arraycopy(strCopy, 0, strCopy, strCopyLen, strCopyLen);
                strCopyLen <<= 1;
            }
        }
        return new String(array);
    }

    @Benchmark
    void martinRepeat(long reps)
    {
        for (int i = 0; i < reps; i++)
        {
            String x = martinRepeat(originalString, count);
            if (x.length() != (originalString.length() * count))
            {
                throw new RuntimeException("Wrong length: " + x);
            }
        }
    }

    private static String martinRepeat(String string, int count)
    {
        final int len = string.length();
        final int size = len * count;
        final char[] array = new char[size];
        string.getChars(0, len, array, 0);
        int n;
        for (n = len; n < size - n; n <<= 1)
        {
            System.arraycopy(array, 0, array, n, n);
        }
        System.arraycopy(array, 0, array, n, size - n);
        return new String(array);
    }
}
